Swing arms are typically used on vehicles where a single wheel, as opposed to two wheels connected by an axle, is fixed to a vehicle frame. Swing arms are especially common in motorcycle design, where one or both wheels are attached to the vehicle frame through a swing arm. The primary purpose of such a swing arm is to provide a strong structural connection of the wheel to the vehicle frame while withstanding significant forces imposed by movement of the vehicle and loads carried by the vehicle. Furthermore, many swing arms have the additional purpose of providing a structure through which a wheel's non-rotational movement can be decelerated and dampened by means of a suspension system, thus imposing smaller stresses on vehicle frame members and increasing passenger comfort.
In the case of a motorcycle, a swing arm may be used at the rear side of the vehicle to pivotally fix and suspend a driven wheel. Often the wheel is driven by a system of gears and sprockets connected with a driving belt or chain. In such an application, the swing arm's design is affected considerably by the need to incorporate driving components and the need to account for the dynamics of driving a suspended, load-bearing wheel. The swing arm may attach to one or two sides of the wheel's rotational axis in order to pivotally fix the wheel to the vehicle frame.
Three-wheeled vehicles are gaining popularity as their unique aesthetics and design become more widely recognized. A three-wheeled vehicle usually requires a swing arm based on the fact that at least one of the three wheels it utilizes must be at the rear of the vehicle while the other two balance the vehicle by being at the front (or vice versa). However, it is advantageous to drive the pair of two wheels rather than the single wheel for the benefit of increased traction and proximity to the engine. Since three-wheeled designs are uncommon, a swing arm design and manufacturing procedure must also accommodate low production quantities and costs while maintaining tight tolerances.
The majority of swing arms in the art are used on vehicles which drive the single wheel attached to the swing arm using a driving belt or chain. In addition, swing arms do not commonly have inherent features (rather than external ones) which accommodate and protect wheel assembly components (wires, brake lines, etc.) which must traverse the distance between the vehicle frame and the wheel assembly fixed to the swing arm. Furthermore, even minor collisions with current swing arms cause sometimes irreparable damage to the vehicle frame. Thus there is room for improvement to swing arms.